1. Field of the Invention
The present invention relates to an ion implantation apparatus and an ion implantation method.
2. Description of the Related Art
The following will describe a typical configuration of an ion implantation apparatus with reference to FIG. 1. In FIG. 1, ions are extracted as an ion beam 52 by an extraction electrode 51 from an ion source 50. The extracted ions are analyzed by a mass analysis magnet 53 and a resolving aperture member 54 and a required ion species is selected. The selected ions are implanted into a wafer 55. The resolving aperture member 54 serves as a mass analysis slit. On a beam line, a shower tube 56 for showering plasma is arranged between the resolving aperture member 54 and the wafer 55. The shower tube 56 is mounted with an arc chamber 57. The arc chamber 57 has an opening therein which faces the beam line side. A Faraday cup 58 for use in measurement of a beam current is provided in such a manner that it can advance onto and retreat from the beam line. That is, the Faraday cup 58 is placed on the beam line when the ion beam is set up (as indicated by a dash-and-dot line in FIG. 1) and placed off from the beam line at the position of a solid line in FIG. 1 when the ions are being implanted. On the back side of the wafer 55, a Faraday cup 59 is arranged so that measurement may be possible during ion implantation.
FIG. 2 is an enlarged view for showing the downstream side of the resolving aperture member 54 in FIG. 1. Although not shown in FIG. 1, components shown in FIG. 1 are arranged in a vacuum chamber 60 as shown in FIG. 2. The arc chamber 57 incorporates therein a filament 57-1. To the filament 57-1 are there connected a filament power source 57-2 and an arc power source 57-3. Furthermore, the arc chamber 57 is arranged in such a manner that a predetermined gas can be introduced into it from a gas supply system 57-4. The shower tube 56, the arc chamber 57, and the arc power source 57-3 are each connected to the ground. In this configuration, in the immediate vicinity of the downstream side of the resolving aperture member 54 is there arranged at least one aperture member 61. The Faraday cup 58 can be advanced onto and retreated from the beam line by a drive device 63 which is mounted outside the vacuum chamber 60.
The following will describe a method of extraction of electrons from the plasma shower. The electrons are specifically extracted from the plasma shower as follows.
(1) Generation of Arc
When a large current is flown through the filament 57-1, the filament 57-1 is heated to 2000xc2x0 C. or higher, to emit thermions. The arc chamber 57 is supplied with a gas such as Ar from the gas supply system 57-4 and also supplied with an arc voltage of a few tens of volts with respect to the filament 57-1. Then, the thermions are accelerated to collide with atoms of the gas, thus generating new thermions. This electron amplification action generates plasma between the filament 57-1 and the arc chamber 57.
(2) Extraction of Electrons by Use of Beam Potential
When an ion beam passes by outside the opening in the arc chamber 57 in a condition where plasma is being generated stably in the arc chamber 57, a positive potential of the ion beam extracts electrons from the plasma which is present in the arc chamber 57. These extracted electrons are accelerated toward the ion beam. These electrons collide with neutral gas atoms which have not been ionized in the arc chamber 57 and ejected through the opening in the arc chamber 57, thus generating plasma again between the arc chamber 57 and the ion beam. This is called a plasma bridge (which is indicated by a reference numeral 65) and has an effect of supplying the ion beam with such a quantity of electrons as to exceed a space charge limited current.
Next, characteristics of extraction of electrons from a plasma shower are described. For example, if the magnitude of a beam current increases, the positive potential of the ion beam increases. As a result, the quantity of electrons which are extracted from the arc chamber 57 increases, thus increasing also the quantity of electrons which are supplied to the ion beam. By such autonomous control, in a plasma shower system, electrons which are abundant enough to neutralize the positive charge of the ion beam are extracted from the plasma shower, thus restraining the positive charging of the wafer 55. That is, the plasma shower system comprised of the shower tube 56 and the arc chamber 57 serves as a charge neutralization apparatus which is for restraining charge.
The following will describe various problems of the above-mentioned conventional technologies.
(1) Effects of Ion Beam Diameter
An ion implantation apparatus employs an ion beam of a variety of ion species, energy levels, and beam currents. The diameter of such an ion beam varies with beam conditions and beam generating conditions.
The arc chamber 57 is mounted at such a position that it may not be collided with an ion beam which has the maximum design diameter. This is done so in order to prevent such a problem from occurring that the beam current would decrease or particles would be generated if the ion beam collides with the arc chamber 57.
If a beam diameter D1 varies at the position of the arc chamber 57, a distance between the opening in the arc chamber 57 and the ion beam also varies and hence the magnitude of an electric field varies. Accordingly, if the beam diameter D1 varies, the quantity of electrons which are supplied to the ion beam varies. For example, if such beam conditions are applied that the beam diameter D1 is liable to decrease, there occurs an insufficiency in quantity of electrons which are supplied from the plasma shower, thus making it impossible to sufficiently suppress positive charging of the wafer 55 in some cases. In order to solve this problem, there may be considered such a method as to vary the power of the plasma shower corresponding to the beam diameter D1. This method, however, requires for its implementation a beam diameter measurement mechanism, a feedback circuit, etc., thus complicating the plasma shower system more than necessary.
(2) Effects of Position of the Arc Chamber 57
The plasma shower is normally arranged on the downstream side of the resolving aperture member 54 where the ion beam is converged, for example, between the wafer 55 and a suppression electrode, that is, the aperture member 61. The plasma shower, however, may be arranged in some cases in the immediate vicinity the wafer 55 so that the wafer may be supplied with electrons easily.
As is clear from FIG. 2, a variation d1 in value of the beam diameter D1 at the position of the plasma shower increases as the plasma shower becomes more distant from the resolving aperture member 54 in a beam axial direction. Accordingly, as the distance between the arc chamber 57 and the ion beam increases in a condition where the arc chamber 57 is separated from the resolving aperture member 54, the quantity of electrons which are supplied from the plasma shower becomes insufficient, thus making it impossible to suppress positive charging of the wafer 55 in some cases.
Next, the Faraday cup 58 is described.
(1) Device Layout Along the Beam Line
As described above, on the downstream side of the resolving aperture member 54 is there arranged the Faraday cup 58 to measure a beam current when the ion beam is set up. The Faraday cup 58 is intended to monitor the beam current, to adjust ion source parameters, thus obtaining a desired ion beam. Furthermore, on the downstream side of the Faraday cup 58, that is, between the Faraday cup 58 and the wafer 55 is there arranged the shower tube 56 to shower plasma, which serves as a charge neutralization apparatus.
When the ion beam is set up completely, the Faraday cup 58 is moved off from the beam line. Then, the ion beam passes through the plasma shower and is transported to the wafer 55, where the ions are implanted into the wafer 55.
It is to be noted that after passing through the resolving aperture member 54, the ion beam diverges. For this reason, as the distance between the resolving aperture member 54 and the wafer 55 increases, the ion beam comes to collide with the shower tube 56 etc., thus being lost more. This loss increases particularly with a low energy beam, thus leading to such a problem in some cases that a throughput may decrease owing to a decrease in the magnitude of the beam current or the ion beam may collide with the shower tube 56 etc.
One of the factors for an elongated distance between the resolving aperture member 54 and the wafer 55 is a problem of an arrangement of the Faraday cup 58 in the beam line. The Faraday cup 58 is moved in such a manner that it may be used only when the ion beam is being set up and, during ion implantation, be moved off from the beam line. The region in the beam line in which the Faraday cup 58 exists becomes a blank when the ions being implanted, thus elongating the beam line.
In view of the above, it is an object of the present invention to provide an ion implantation apparatus and method which can avoid extraction of electrons from a plasma shower from being influenced by a variation in ion beam diameter.
It is another object of the present invention to provide an ion implantation apparatus and method which can suppress loss of an ion beam particularly at a low energy level.
In an ion implantation method to which the present invention is applied, when an ion beam extracted from a ion source is transported to be implanted into a processing-subject substrate, the ion beam is caused to pass through a charge neutralization section in a transportation section on the upstream side of the processing-subject substrate.
An ion implantation method according to an aspect of the present invention features that an ion beam is neutralized by a charge neutralization section at such a position that it is brought nearest the ion beam.
This position which is nearest the ion beam in the present ion implantation method is intended to be such a position that the beam diameter may be smallest there or to be in the immediate vicinity of the downstream side of the position.
In the present ion implantation method, the position which is nearest the ion beam is intended to be a position in the immediate vicinity of the downstream side of a position where the beam diameter becomes smallest and also the position of the charge neutralization section is intended to be variable corresponding to the beam diameter.
In the present ion implantation method, furthermore, on the upstream side of the charge neutralization section is there arranged a resolving aperture member for converging and diverging a beam. Accordingly, the position in the immediate vicinity of the downstream side of a position where the beam diameter becomes the smallest is intended to be on the downstream side of the resolving aperture member.
In the present ion implantation method, furthermore, the charge neutralization section includes a shower tube and an arc chamber combined therewith. A length of the shower tube is made shorter in a beam axis direction.
In the present ion implantation method, furthermore, the shower tube has a minimum required inner diameter.
In the present ion implantation method, furthermore, along a beam line between the shower tube and a processing-subject wafer may there be arranged an intermediate tube in such a manner as to continue to the shower tube.
In the present ion implantation method, furthermore, the arc chamber may be variable in position in a direction perpendicular to a beam axis corresponding to a beam diameter or intensity.
In the present ion implantation method, furthermore, the arc chamber may be variable in position in the beam axis direction corresponding to a beam diameter or intensity, so as to be arranged nearest the ion beam.
In the present ion implantation method, furthermore, the diameter of the shower tube may be variable corresponding to a beam shape, position, or size.
In the present ion implantation method, furthermore, the length of the shower tube may be variable corresponding to a beam shape, position, or size.
In the present ion implantation method, furthermore, the shower tube may be variable in position in the beam axis direction corresponding to a beam shape, position, or size.
In the present ion implantation method, furthermore, a beam measurement portion may be arranged in a transportation section on the upstream side of a processing-subject substrate. In this case, the beam measurement portion and the charge neutralization section may be interchangeable at the same position on the beam line.
In the present ion implantation method, furthermore, on the upstream side of the charge neutralization section may there be arranged the beam convergence/resolution resolving aperture member. Accordingly, the position which is nearest the ion beam may be present in the resolving aperture member. In this case, on the downstream side of the resolving aperture member is there provided a beam measurement portion in such a manner that it can advance onto and retreat from the beam line. In this case, furthermore, on the downstream side of the resolving aperture member may there be arranged an intermediate tube.
In an ion implantation apparatus to which the present invention is applied, when an ion beam extracted from a ion source is transported to be implanted into a processing-subject substrate, the ion beam is caused to pass through a charge neutralization section in a transportation section on the upstream side of the processing-subject substrate.
The ion implantation apparatus according to an aspect of the present invention features that the charge neutralization section is arranged at a position which is nearest the ion beam.
In the present ion implantation apparatus, the position which is nearest the ion beam is intended to be such a position that the beam diameter may be smallest there or to be its immediate vicinity of the downstream side of the position.
In the present ion implantation apparatus, the position which is nearest the ion beam is intended to be such a position in the immediate vicinity of the downstream side that the beam diameter may be the smallest. Furthermore, the present ion implantation apparatus is provided with a drive unit which makes the position of the charge neutralization section variable corresponding to the beam diameter.
In the present ion implantation apparatus, furthermore, on the upstream side of the charge neutralization section is there arranged the resolving aperture member for converging and diverging the ion beam. Accordingly, the position in the immediate vicinity of the downstream side of a position where the beam diameter becomes the smallest is intended to be on the downstream side of the resolving aperture member.
In the present ion implantation apparatus, furthermore, the charge neutralization section includes the shower tube and the arc chamber combined therewith. A length of the shower tube is made shorter in a beam axis direction.
In the present ion implantation apparatus, furthermore, the shower tube has a minimum required inner diameter.
In the present ion implantation apparatus, furthermore, along a beam line between the shower tube and a processing-subject wafer may there be arranged the intermediate tube in such a manner as to continue to the shower tube.
In the present ion implantation apparatus, furthermore, the drive unit includes a drive mechanism which makes variable the position of the arc chamber in the direction perpendicular to the beam axis corresponding to the beam diameter or intensity.
In the present ion implantation apparatus, furthermore, the drive unit includes a drive mechanism which makes variable the position of the arc chamber in the same direction as the beam axis direction corresponding to the beam diameter or intensity. In this case, the arc chamber can be arranged at a position which is nearest the ion beam.
In the present ion implantation apparatus, furthermore, the shower tube may be comprised of at least two members which are divided in the same direction as the beam axis direction. In this case, one of these at least two divided members has a cross section which is a little smaller than that of the other. The drive unit may include a drive mechanism which makes variable the diameter of the shower tube by bringing these two divided members close to or separate them from each other corresponding to the beam shape, position, or size.
In the present ion implantation apparatus, furthermore, the shower tube may be comprised of at least two members which are divided in a direction perpendicular to the beam axis. In this case, one of these at least two divided members has a diameter which is a little smaller than that of the other. The drive portion may include a drive mechanism which makes variable the length of the shower tube by moving at least one of these two divided members in the beam axis direction corresponding to the beam shape, position, or size.
In the present ion implantation apparatus, furthermore, the drive unit may include a drive mechanism which makes variable the position of the shower tube in the same direction as the beam axis direction corresponding to the beam shape, position, or size.
In the present ion implantation apparatus, furthermore, the beam measurement portion may be arranged in a transportation section on the upstream side of a processing-subject substrate. Moreover, an interchanging drive device is provided which makes it possible to interchange the beam measurement portion and the charge neutralization section with each other at the same position on the beam line.
In the present ion implantation apparatus, furthermore, on the upstream side of the charge neutralization section is there arranged the beam convergence/resolution resolving aperture member. In this case, the position which is nearest the ion beam may be present in the resolving aperture member. In this case, on the downstream side of the resolving aperture member may there be provided a beam measurement portion in such a manner that it can advance onto and retreat from the beam line. In this case, furthermore, on the downstream side of the resolving aperture member may there be arranged the intermediate tube.